1. Field of the Invention
The present invention relates to a wafer drying apparatus in which a holding case accommodating a plurality of semiconductor substrate wafers is rotated on a turntable and the wafers are dried with water being scattered therefrom by centrifugal force, and more particularly to a balancing mechanism for the turntable used in the wafer drying apparatus.
2. Description of the Related Art
A conventional wafer drying apparatus of the kind to which the present invention relates is first explained to assist the understanding of the invention. FIGS. 1A and 1B diagrammatically show an example of the conventional apparatus, FIG. 1A being a sectional view thereof and FIG. 1B being a partially broken perspective view thereof. As shown therein, the apparatus includes a plurality of cradles 2 in each of which the holding case 6 accommodating a plurality of wafers 16 is placed and each of which is allowed to swing vertically and is mounted in the turntable 8 through a supporting member 9 facing to each other with a rotary axis 10 being in the center; a drying chamber 5 which surrounds these cradles 2 and has an exhaust opening 7 at a lower part thereof and a cover 4 to close an upper part; and a balancing mechanism 3 which, in order to adjust the balancing of the rotation of the turntable 8, moves and adjusts the supporting member 9 of the cradles 2 in the radial direction of the rotation of the turntable.
In the operation of drying the wafers 16 using the above wafer drying apparatus, first the holding cases 6 each accommodating the wafers 16 are placed in the empty cradles 2 while the turntable 8 is in a stopped state (FIG. 1B). When the turntable 8 is caused to rotate at a high speed by the rotary axis 10, the cradles 2 rotate 90.degree. about a supporting axis by the centrifugal force and change their positions as shown in FIG. 1A. The water adhered on the wafers 16 scatters by the centrifugal force and is exhausted from the exhaust opening 7 at the lower part of the drying chamber 5.
In the conventional wafer drying apparatus as explained above, there is provided a balancing mechanism 3 in order to attain the rotating balancing of the turntable 8 in the case where the number of wafers placed in one holding case 6 is different from that in the other holding case 6 opposing thereto.
The balancing mechanism 3 includes an eccentric cam 3a carried by the rotary axis of the supporting portion which projects from the surface of the turntable 8, a cam driving axis 3b engaged in a slit provided in the eccentric cam 3a. When the eccentric cam 3a is caused to rotate by the upward/downward movement of the cam driving axis 3b, the sliding portions touching the eccentric cam 3a at the right and the left are caused to slide to the right and the left by pressing force due to the eccentric cam 3a. Consequently, the supporting member 9 mounted on the sliding portions move in the radial direction of the rotation of the turntable whereby the rotating balance of the turntable 8 is achieved.
In the conventional wafer drying apparatus explained above, there was a problem that, while the turntable is being rotated at a high speed, the eccentric cam in the balancing mechanism touches with and slides on the sliding portion so that contaminants are generated from the sliding portion. Further, since the balancing mechanism that generates the contaminants is located in the same holding case that accommodates wafers, a problem is that, during the rotation of the turntable, the contaminants scatter within the entire drying chamber and adhere on the wafers, resulting in the contamination of the wafers and the deterioration of production yields.
An example of the conventional wafer drying apparatus in which a means is provided to prevent the generation of contaminants is disclosed in Japanese Patent Application Kokai Publication No. Sho 60-154624. The disclosed device is one which does not include a balancing mechanism but is arranged such that two wafer holding cases are disposed evenly at the inner periphery of the rotor, and the water on the wafers is expelled by the rotation of the rotor at a high speed. The arrangement includes a rotor driving chamber which surrounds the rotor driving section for the rotation of the rotor and which is separated from the drying chamber. The air in the vacant section of the rotor driving chamber is exhausted from the exhaust opening thereof, and it is so arranged that the rotating driving chamber is in a vacuum state with respect to the drying chamber thus preventing the entry of the contaminants into the drying chamber.
However, in the above wafer drying apparatus, since the rotor driving chamber is in a vacuum state with respect to the drying chamber, the cleaning water in which particles are mixed flows not only into the water exhaust section but also into the portion where the rotary axis is inserted, thereby causing the corrosion of the rotor mechanism or the plugging, by the particles, of the portion where the rotary axis is inserted. This makes the apparatus unendurable to a long time operation. Also, for creating a negative pressure in the rotor driving chamber, it requires an air exhaust means connected to the water exhaust section, and this adds to the cost of the manufacturing equipment.